This invention relates to a composite type conductive polymer, more particularly a composite type conductive polymer having a phenylene vinylene backbone. The present invention also relates to a process of producing an aromatic compound which can be used as a monomer for synthesizing the composite type conductive polymer. Conductive polymers are useful in the electric and electronic industries as various conductive materials or optical materials providing parts demanding high processability, such as electrodes, sensors, electronic display devices, nonlinear optical devices, and photoelectric devices, antistatic agents, automotive parts, electromagnetic shields, and the like.
Poly(phenylene vinylene)s (hereinafter abbreviated as PPVs) have been engaging attention in the field of conductive polymers. PPVs are polymers having a phenylene vinylene skeleton (structure) in the main chain. On being doped with a dopant, PPVs form a charge transfer complex which exhibits electric conductivity and maintains high conductivity of at least about 101 S/cm.
However, conductive PPVs reduce the conductivity below a practical level on about one day standing in the air probably because the dopant is released or deteriorated by the influences of the air. PPVs having a 1,4-phenylene chain (poly (para-phenylene vinylene) s), in particular, have a rigid linear molecular structure which tends to refuse a dopant""s entering between molecules so that a dopant once accepted is liable to be released or deteriorated.
Having a linear molecular structure, PPVs possess so strong an intermolecular force that they are insoluble in most solvents. For the same reason, PPVs have no melting point. In other words, such insoluble and non-melting PPVs have poor processability and poor molding properties.
In the light of these circumstances, it is an object of the present invention to provide a conductive PPV which, when doped with a dopant, does not cause the dopant to be released or deteriorated and exhibits satisfactory processability.
As a result of extensive investigations, the present inventors have found that introducing a bend into the linear structure of the PPV""s backbone results in reduction of the rigidity, which would suppress release and deterioration of the dopant. Based on this finding, the present inventors have reached the present invention.
The present invention provides a composite type conductive polymer having a phenylene vinylene backbone with a condensed hydrocarbon ring system introduced into the backbone to form a bend in the linear structure of the backbone.
Such a modified structure has reduced rigidity so that an external dopant enters between polymer molecules easily. Further, because the bend in the backbone reduces the intermolecular force, the polymer gains solvent solubility and satisfactory processability.
The condensed hydrocarbon ring system which can be introduced into the linear structure preferably includes those derived from naphthalene derivatives and anthracene derivatives.
In a preferred embodiment, the present invention provides a composite type conductive polymer having from 1 to 9999 of a phenylene vinylene backbone and from 1 to 9999 of a naphthylene vinylene backbone, wherein a total number of the phenylene vinylene backbone and the naphthylene vinylene backbone is from 10 to 10000.
In order to ensure protection for a dopant and improvement of processability, the naphthylene group in the preferred embodiment is desirably selected from a 1,5-naphthylene group, a 1,6-naphthylene group, a 2,5-naphthylene group, a 2,6-naphthylene group, and a 2,7-naphthylene group, which will make an appreciable bend in the backbone.
It is preferred that the ratio of the phenylene vinylene backbone to the naphthylene vinylene backbone in the above structure of the preferred embodiment be from about 3:7 to 7:3. With too high a proportion of the phenylene vinylene backbone, it is difficult to get much effect in protecting a dopant and improving the processability. Too high a proportion of the naphthylene vinylene backbone, on the other hand, tends to compromise the characteristics inherent to PPVS.
The present invention also provides a process of producing an aromatic compound as a monomer for synthesizing the composite conductive PPV of the invention. That is, the invention provides a process of producing an aromatic compound having a halomethyl group bonded to the benzene nucleus thereof, which starts with an aromatic compound having a carbon atom bonded to the benzene nucleus and comprises forming a halomethyl group through a substitution reaction on the carbon atom. According to the process, a desired aromatic compound can be obtained in good yield. This will make it possible to synthesize the composite type conductive polymer of the invention efficiently.
In one embodiment of the process, an aromatic compound having a carboxyl group bonded to the benzene nucleus is used as a starting material, and the process comprises:
(1) a halogenating step in which the hydrogen of the carboxyl group is substituted by a halogen to form a carboxyl halide,
(2) a carboxymethylating step in which the halogen of the carboxyl halide is substituted with a methyl group to form a carboxymethyl group,
(3) a hydroxymethylating step in which the hydroxyl group of the hydroxymethyl group is substituted with a halogen to form a halomethyl group, and
(4) a halomethylating step in which the hydroxyl moiety of the hydroxymethyl group is substituted with a halogen to form a halomethyl group.
In another embodiment of the process, an aromatic compound having a methyl group on the benzene nucleus thereof is used as a starting material, and the process comprises substituting one of the hydrogen atoms of the methyl group with a halogen.